The present invention relates to a front suspension apparatus adapted to suspend or support a front wheel provided as a steering road wheel, so as to enable the front wheel to move (have a suspension stroke) in the vertical direction relative to a vehicle body.
As a front suspension apparatus for a vehicle, Japanese Patent Application Publication No. 2003-136927 discloses a previously proposed double-pivot type front suspension apparatus. Since this front suspension apparatus is of double-pivot type in which two lower link members suspend an axle member from the vehicle body, an imaginary pivot point is set on a point at which extension lines of both lower link members intersect with each other. By adjusting a relationship of relative positions between the two lower link members, the position of the imaginary pivot point can be freely set so that a degree of freedom to set a kingpin axis can be enhanced.
The double-pivot type front suspension apparatus disclosed in the above patent application can adjust a lateral-force compliance steer amount by means of a fluctuating (swinging) direction and a fluctuating amount of two lower link members. Hence, a bush stiffness at each of vehicle-body-side attaching points and axle-member-side attaching points of these lower link members can be determined only by a requirement of lateral stiffness. Therefore, two performances of the “adjustment of lateral-force compliance steer amount” and the “enhancement of lateral stiffness” can be achieved at high order. Thus, with respect to these both characteristics, “degree of freedom to allocate static characteristics” is increased in this technique.
In the case of a suspension apparatus using an A-shaped arm member instead of the two lower link members, the lateral stiffness and the lateral-force compliance steer amount can be adjusted only by the bush stiffness at each of vehicle-body-side attaching points and an axle-member-side attaching point of the A-shaped arm member. Accordingly, when trying to enlarge the lateral stiffness by enhancing the bush stiffness, the lateral-force compliance steer amount becomes too small. On the other hand, when trying to enlarge the lateral-force compliance steer amount by reducing the bush stiffness, the lateral stiffness becomes insufficient. As just mentioned, two performances of the “adjustment of lateral-force compliance steer amount” and the “enhancement of lateral stiffness” cannot be achieved at high order. Thus, in this case, with respect to these both characteristics, the “degree of freedom to allocate static characteristics” is low, so that a sacrifice of any one of these both characteristics cannot be avoided.
Contrary to the above case, in the double-pivot type front suspension apparatus as disclosed in the above patent application, the lateral-force compliance steer amount can be adjusted by the fluctuating direction and fluctuating amount of the two lower link members, alone, as mentioned above. Then, the lateral stiffness can be set by the bush stiffness at each of vehicle-body-side attaching points and axle-member-side attaching points of the lower link members, alone, as mentioned above. Namely, the “degree of freedom to allocate static characteristics” is high with respect to these both characteristics, so that the above-mentioned problem can be avoided.
Therefore, the double-pivot type front suspension apparatus has the above-mentioned advantage related to the high degree of freedom to set the kingpin axis, and the advantage that the “degree of freedom to allocate static characteristics” is high with regard to the “adjustment of lateral-force compliance steer amount” and the “enhancement of lateral stiffness”.